Power supply unit

ABSTRACT

A plug device with a built-in power supply of switch mode power supply type is disclosed. The plug device comprises a printed circuit board upon which a high-frequency transformer, a low-voltage capacitor and other components which make up a switch mode power supply are arranged. A first isolating barrier extends form the housing in between the high-frequency transformer and said low-voltage capacitor. A third isolating barrier (46) extends form the housing and into a first slot in the printed circuit board and a fourth isolating barrier extends from said housing and into a second slot in the printed circuit board. These slots are placed between the high-voltage and low-voltage connection terminals of the high-frequency transformer. A second isolating barrier extends from said housing and between the high-frequency transformer and the printed circuit board and beneath said high-frequency transformer.

FIELD OF THE INVENTION

The invention relates to a plug device with an built-in power supply ofa switch mode power supply type (SMPS type) or a power supply unitcomprising a printed circuit board (PCB) upon which a high-frequencytransformer, a low-voltage capacitor and other components are arranged,said device further comprising a housing and at least two inputconnectors adapted for insertion into a socket such as a wall socket.

All over the world different standards for electronic devicesexist-though in some places the standards are considerably lower than inothers-and AC/DC adapters must comply with these standards. One set ofsuch standards are the IEC standards. IEC 60950 describes the minimumrequirements for electrical equipment with regard to isolation andminimum distances between components with different voltage levels. IEC61000 describes minimum requirements for electromagnetic compatibility(EMC). Usually, some standards are also set out for the shape ofelectric/electronic devices, In the case of plug devices, the standardEN 50075 is set out and applies to plug devices in the EU. In thefollowing, the plug size will be referred to as a European type plug.

The plug device is of small physical dimensions, thus requiring specialattention to the arrangement of components in order to comply withstandards like the [IEC] standards. This is because the outer surface ofcapacitors usually is made from a metal like aluminium, which is fullyor partially covered by some plastic or ceramic material. This materialhas insulating properties, but does not comply with any specificstandards and thus the surface of the capacitor must be regarded as aconducting surface. This also applies to the core of the high-frequencytransformer.

The core of a high-frequency transformer is usually made from a materiallike ferrite. Ferrite has low electrical conductivity, however, it isnot low enough to be regarded as an insulator. Thus, the core of thetransformer must also be regarded as a conducting surface.

DESCRIPTION OF THE PRIOR ART

Over time there have been several inventions focused on integratingAC/DC adapters into the mains plug used for the mains power supply.These adapters are very useful because many electronic devices require apower supply with a low-voltage (typically, 3-15V) and a low powerconsumption (1-20W). External power supplies are also a way of reducingthe overall costs and thus the electronic device may have to be designedfor use with only one voltage. The external power supply is then adaptedto convert different voltages and frequencies to a specified DC voltage.However, the latter has been accomplished with a plug device of theEuropean type only to a degree, which primarily is due to the physicalsize of the converting circuit which previously tended to be large andbulky.

Today, most low-power AC/DC adapters use a technology of the lineartype. The linear type converter consists of a transformer for reducingthe voltage to an appropriate level, optionally 1 or 4 diodes forrectifying the voltage and a capacitor for smoothening the voltage.Optionally, there may be one or more components for limiting the maximumoutput voltage. Most of the components are passive, leading to thequality of the output voltage being dependent on the load. This alsoleads to a degree of over-compensation by making the components large.The use of a transformer also provides a galvanic separation between theinput voltage and the output voltage. It is also the linear typeconverter which, on most occasions, has been used to make AC/DC adapterswith a plug-like shape fitting into a wall socket to be used withelectronic equipment such as mobile phones and the like.

U.S. Pat. No. 4,273,406 describe an AC/DC adapter accommodated within aplug device. In this adapter, a linear type transformer is received in atwo-part cylindrical casing fastened with a screw. There are severaldrawbacks of said invention due to its application of a large lineartype transformer. The most severe drawback is that the casing is largeand heavy. Furthermore, the plug is not easily fitted into the Europeantype sockets.

Similarly, EP 0493080 describes a plug with a linear type transformer.The plug device is used especially for medical equipment and hence avery special configuration of the input connectors (coding of plug andsocket) is used. However, the input connectors are easily adapted forthe European type sockets. The only difference between EP 0493080 andU.S. Pat. No. 4,273,406 is that the plug device is “long and thin”instead of “short and fat” due to the internal arrangement of thecomponents. Even though several plugs may easily fit in sockets arrangedclosely together, the volume of the plug is not changed in anysignificant degree.

WO 01/08270 describes an AC/DC adapter of a type similar to U.S. Pat.No. 4,273,406. The invention according to WO 01/08270 fits into theEuropean type sockets. However, this is achieved by having a sectionwith the input connectors adapted for insertion into the socket. Theremaining components are housed in a large compartment attached to thissection.

Today, the converting circuit technology for AC/DC adapters also usesother newer types of converters which employ high-frequency switchingtechnology. The switching technology provides many benefits over thelinear type. These include size, weight and efficiency. It is alsopossible to manufacture AC/DC adapters which have ‘universal’ input,meaning that the adapter may work with many different voltages andvoltage ranges, e.g. ranging voltages from 80V to 250V and frequenciesranging from 40 Hz to 70 Hz.

However, despite the obvious advantages of switch mode technology, eventoday the old-fashion linear power supply still dominates the market forAC/DC adapters with a wattage below 10 watts (ref: U.S. Pat. No.5,469,334). The reason is that the manufacturing cost of a SMPS adapteris still considerably higher than for a comparable linear power supplyin the same wattage class. The linear power supplies are also producedin very high numbers making manufacturing costs low.

Keeping the production costs in mind combined with today's design ofswitch mode power supplies-which is usually less than half the size of alinear adapter-it becomes more evident why the switching technology hasnot yet been employed in a larger number of low wattage AC/DC adapters.

The Flyback converter is a preferred type of SMPS due to itshigh-frequency transformer, which provides a galvanic separation. Othertypes of SMPS may also be used. The switching of the transistor isusually controlled by some Pulse Wide Modulation (PWM) which includessome regulator means for stabilizing the voltage.

The sizes of the inductor/transformer and capacitor are based on therequired load and the switching frequency of the transistor (energy percycle). Thus a high frequency results in smaller components because lessenergy is transferred per cycle.

Of all the above mentioned techniques the Flyback converter is preferredbecause it provides a galvanic separation between the supply voltage andthe output voltage.

The Flyback converter also enables several different output voltages,each galvanically separated from each other. The types of SMPS which donot have a built-in galvanic separation may employ a separationtransformer in order to obtain a galvanic separation. However, thissolution adds both an extra component and further disadvantages inrelation to the linear type of converter.

A plug device was described in “Machine Design” 9,62 (1990). Thisinvention features a SMPS in a mains plug which converts mains ACvoltage into low-voltage DC. The invention uses an integrated circuit(IC) which combines a high-voltage MOSFET and a digital circuitry forswitching. All electronic components for the adap-ter are arranged on asingle PCB arranged inside a plug,and perpendicular to the two inputconnectors. The described plug device has a SMPS type AC/DC adapterfitting within the dimensions of a plug device. However, the articleprovides no solutions to the problems associated with the small size.

WO 94/06177, equivalent to German utility model G 9320893 U1, describesa European type plug with an built-in power supply. The described SMPSis a Flyback converter. However, the publication does not describe howthe SMPS can be arranged inside the plug device and at the same timecomply with the required standards. WO 94/06177 uses a special carrierplate on which the PCB is mounted.

The PCB features an essential hexagonal shape and fits to the innercontour of the plug device. Furthermore, the PCB is arranged on top ofthe carrier plate and contains all the components for the adapter.

Prior art AC/DC adapters have not been able to exploit the advantages ofthe switching technology while at the same time feature a compact designwhich fits into the Euro-plug for the mains. The two main reasons arethat as the dimensions shrink, a new set of problems arrive due to therequired primary side to secondary side isolation and problems inrelation to EMC arise due to the switching technology.

Several problems within different technical fields will have to besolved simultaneously in order to construct a plug device with smalldimensions, preferably of the European type size or even smaller.

One of the problems with this type of SMPS is that the creepage andclearance distances must be approximately 5 mm in order for the productto be approved with the safety standards. One solution is to encapsulatethe electronic components using a technology like macro-melt or pottingtechniques. Macro-melt infuses the plug with a liquid or semi-liquid,which hardens or stays as a semi-liquid and forms insulating barriersbetween the components. The method allows components to be arranged veryclosely together. This is an expensive method for insulating thecomponents and it is difficult to guarantee that no air pockets willoccur where the liquid separates the primary and secondary circuits. Themacro-melt method may also significantly change the way the componentsdissipate heat.

SUMMARY OF THE PRESENT INVENTION

The objective of the invention is to provide a power supply unit whichfits into an plug device, like a European type plug, as a mains adapter.Furthermore, an AC/DC power supply must fulfil the requirements ofvarious safety and EMC regulations as stated in the above mentionedstandards in order to be approved. By using isolating barriers it ispossible to manufacture a plug device with a built-in adapter of theSMPS type which fits within the dimensions of a European type plug andwhich at the same time complies with the standards for a device of thistype. It is even possible to use standard components. Even a small risein production costs in relation to other SMPS's marketed today should beavoided if possible as the SMPS AC/DC adapters will compete with theold-fashion linear adapters as well as other AC/DC adapters with SMPStechnology. The price will thus be an important factor.

This means that expensive and new components like Oscon capacitors,multi layer ceramic capacitors (MLCC) or tantal capacitors should beavoided if possible. The rule of the thumb with price sensitiveelectronic products is to use old fashion components which are widelyavailable by several suppliers instead of state-of-the-art technology.The same applies to production technology where standard productionmachinery is widely available. The use of new technology may, however,benefit the invention and will make it possible to make the AC/DCadapter even smaller or make an AC/DC adapter of similar physical sizewith higher wattage.

According to a first aspect of the present invention, a power supplyunit is provided comprising:

a housing defining a front end and a rear end,

a pair of pins for cooperating with a mains supply outlet and extendingperpendicularly from a front end wall of the front end of the housing,

a low-voltage cord or a low-voltage connector extending from the rearend of the housing,

a switch mode power supply circuit including a printed circuit board forthe conversion of the mains supply voltage to a low-voltage,

the printed circuit board being mounted within the housing orientedsubstantially parallel with the front end wall having the pins connectedto the one side of the printed circuit board and having the low-voltagecord or low-voltage connector connected to the one side or preferablythe opposite side of the printed circuit board, and

the housing having a cross-sectional configuration between the front endand the rear end, substantially corresponding to and not exceeding thecross-sectional configuration of the front end wall of a Euro-plugaccording to the EN 50075 standard.

According to the basic teachings of the present invention, theintegration of a switch mode power supply circuit into a housing havingdimensions not exceeding the dimensions of a Euro plug according to theEN 50075 standard, is obtained by the use of the printed circuit boardin a position parallel with the front end wall of the housing asdistinct from the prior art integrated power supply units in which theprinted circuit boards have been positioned parallel with the pair ofpins for establishing conductive connection to the mains supply outlet.

According to a second aspect of the present invention, a power supplyunit is provided comprising: a housing defining a front end and a rearend,

a pair of pins for co-operating with a mains supply outlet and extendingperpendicularly from a front end wall of said front end of said housing,

a low-voltage cord or a low-voltage connector extending from said rearend of said housing,

a switch mode power supply circuit including a printed circuit board forthe conversion of the mains supply voltage to a low-voltage, and

said printed circuit board being mounted within said housing orientedsubstantially parallel with said front end wall having said pinsconnected to the one side of said printed circuit board and having saidlow-voltage cord or low-voltage connector connected to said one side orpreferably the opposite side of said printed circuit board.

According to the presently preferred embodiment of the power supply unitaccording to the present invention, the switch mode power supply circuitincluding a first rectifier or mains supply rectifier for receiving themains supply voltage and for converting the mains supply voltage into afirst DC voltage to be output from a pair of outputs of the firstrectifier, a first energy reservoir capacitor connected across theoutputs of the first rectifier for smoothing the first DC voltage, ahigh frequency oscillator or high frequency switch having a pair ofinput terminals for receiving the first DC voltage from the capacitorand for output of a high frequency oscillation voltage from a pair ofoutput terminals to a high frequency transformer for reducing thevoltage of the high frequency oscillation into a low transformer outputvoltage and having a pair of input terminals and a pair of outputterminals, the input terminals being connected to the output terminalsof the high frequency oscillator, the output terminals of the highfrequency transformer being connected to a further rectifier forrectifying the low transformer output voltage and having a pair ofrectifier outputs for connection to a further energy reservoir capacityconnected to the low-voltage cord or the low-voltage connector.

A particular feature of the present invention relates to the provisionof contacting the pair of pins to the printed circuit board andaccording to this particular feature of the present invention, one ofthe pins of the pair of pins for establishing electrical conductiveconnection to the mains supply outlet is connected through a fuse,preferably constituted by a resistor to the printed circuit boardincluding the switch mode power supply circuit.

According to a further feature, the other pin is connected to theprinted circuit board through a spring loaded contact to establishingelectrical conductive connection from the pin to the switch mode powersupply circuit.

A particular aspect of the present invention relates to the abovedescribed isolating problems and according to the teachings of thepresent invention the high frequency transformer is positioned betweenthe two capacitors on the printed circuit board facing away from thepair of pins.

The standards require that the high-voltage side and the low-voltageside be separated in a way that prevents accidental discharges betweenthe high-voltage side and the low-voltage side. As mentioned in IEC60950, this requires a specified minimum of distance through air andthrough isolation between these sides. By inserting an isolating barrierbetween the high-frequency transformer and the low-voltage capacitors,the required distance between the two components becomes smaller.

Another consideration is creepage. Creepage is when the electricalcharge creeps over the surface of an insulator and thus moves anelectrical charge to an unintended position. Arranging the firstisolating barrier between the high-frequency transformer and thelow-voltage capacitor thus increase the surface distance between saidhigh-frequency transformer and said low-voltage capacitor and reducescreepage distance.

As mentioned above, several different topologies for SMPS's exist. To beable to fit an SMPS within the dimensions of a plug, a number of designfeatures must be contemplated. The preferred SMPS topology is theFlyback converter, but many if not most considerations regardingisolation may be transferred to the other topologies. If for example aBuck-converter is used to control the voltage, a separation transformermay be used to lower the voltage to an appropriate level and to give thegalvanic separation.

According to a first preferred embodiment of a plug device according tothe invention in which a low-voltage output cord is attached to saidplug device and adapted for connecting said plug device to a consumer,the first isolating barrier also extends between said high-frequencytransformer and said low-voltage cord. The function of a plug devicerequires that the built-in adapter is connected to an outside consumer.By extending said first isolating barrier it becomes possible to attacha low-voltage cord to the plug device in positions which otherwise wouldbe too close to the high-voltage side.

According to another preferred embodiment of a plug device according tothe invention, a third isolating barrier extends from the housing andinto a first slot in the PCB, a fourth isolating barrier extends fromsaid housing and into a second slot in said PCB and the first and secondslots are arranged between the high-voltage and low-voltage connectionterminals of the high-frequency transformer. By placing isolatingbarriers between the high-voltage and low-voltage connection terminals,it is possible to arrange them closer together, thus making it possibleto use a high-frequency transformer with a more narrow coil form withthe connection terminals arranged closer together. Also, by placing saidisolating barriers in a slot in said PCB, it is possible to usetwo-sided PCB's where said high frequency transformer is arranged onsaid PCB using thru-holes. Thru-holes would otherwise be problematicbecause the connection terminals extend out from opposite sides of saidPCB.

According to another preferred embodiment of a plug device according tothe invention, an optocoupler is arranged on said PCB between said firstand second slots beneath said high-frequency transformer and on the sameside of said PCB as said high-frequency transformer. This allows for theuse of an area of said PCB to be occupied by a component, which spansfrom the high-voltage side to the low-voltage side similar to thehigh-frequency transformer. If said OPTOCOUPLER was not arranged beneaththe high-frequency transformer, it would have to occupy another part ofthe PCB. Thus the above arrangement saves space on the PCB making therequired space on the PCB smaller.

According to another preferred embodiment of a plug device according tothe invention, an OPTOCOUPLER is arranged on said PCB between said firstand second slots beneath the high-frequency transformer and on theopposite side of said PCB as said high-frequency transformer. Thisenables the use of a high-frequency transformer of a surface mounteddevice type (SMD type). The optocoupler functions in the same way withrespect to isolation whether it is arranged on the opposite side of thePCB with respect to said high-frequency transformer instead of betweenthe high-voltage side and the low-voltage side. However, it does notsave space on the PCB.

According to another preferred embodiment of a plug device according tothe invention, a second isolating barrier extends from the housing andbetween the high-frequency transformer and the PCB and any othercomponents arranged on said PCB beneath or approximately beneath thehigh-frequency transformer.

Components near or beneath said high-frequency transformer are either onhigh-voltage potential or low-voltage potential. As mentioned above, thecore of the high-frequency transformer has to be regarded as aconducting surface. Placing the second isolating barrier between thehigh-frequency transformer and the PCB and any other components arrangedon said PCB beneath or approximately beneath the high-frequencytransformer shields the core of said high-frequency transformer.

According to another preferred embodiment of a plug device according tothe invention, a fifth isolating barrier extends from said housing andfully or partially around a fuse component attached between one of saidat least two input connectors and said PCB. The fuse component may beconnected between said -PCB and between either of said input connectors.Depending on the arrangement of said PCB inside said plug device, thefuse component may be too close to the component comprising the SMPS. Byarranging said fifth isolating barrier fully or partially around saidfuse component, a CLOSER spacing between said fuse component and saidcomponents comprising said SMPS is obtained, thus saving space on saidPCB. If said fifth isolating barrier and said fuse component furthermoreare arranged with an offset with regard to the centreline of said PCB,more space is provided for components on said PCB.

According to another preferred embodiment of a plug device according tothe invention, the housing and isolating barriers are moulded as onepiece. Moulding said housing and said isolating barriers as one piecegives an easy way of producing said housing with all of said isolatingbarriers.

According to another preferred embodiment of a plug device according tothe invention, said housing comprises two or more separate piecesadapted for attaching each other and forming a larger element. Dividingsaid housing in two or more pieces makes it easier to close said housingaround said PCB and around the components comprising said SMPS. It isalso possible to provide a separate element upon which the inputconnectors are attached. One way of attaching said separate pieces toeach other could be by gluing or ultrasonic welding them together.

According to another preferred embodiment of a plug device according tothe invention, one or more of the isolating barriers are separate pieceswithin the housing and attached to or held in place by the housing. Byhaving isolating barriers made separate from the housing, it is possibleto use isolating barriers with a complex shape which otherwise would bevery difficult to use if they were an integrated part of the housing.Said isolating barriers are attached to said housing, e.g. by the use ofglue or by holding them in place e.g. by slots or notches in saidhousing.

According to another preferred embodiment of a plug device according tothe invention, said housing and said isolating barriers are constructedfrom materials with different properties. By making said isolatingbarriers from a different material than said housing, it Will bepossible to select the isolating properties of the different parts. Thehousing could have good EMC-SHIELDING properties while said isolatingbarriers only need good electrical isolating properties.

According to another preferred embodiment of a plug device according tothe invention, said slots in said PCB extend all the way over said PCB.This makes it possible to produce a high-voltage circuit and alow-voltage circuit and then decide on the individual arrangementafterwards

According to another preferred embodiment of a plug device according tothe invention, one or more of said isolating barriers are attached to orheld in place by said PCB and not said housing. This gives some of thesame advantages as when said isolating barriers are held in place bysaid housing, but it also gives the freedom of arranging a componentwhich needs isolating in a position where it would be difficult toattach said isolating barriers to said housing.

According to another preferred embodiment of a plug device according tothe invention, one or more of said isolating barriers are an integratedpart of said PCB and not said housing. Some of said isolating barriers,like said third and fourth isolating barriers, could just as well be apart of said PCB. Said PCB has already good electrical insulatingproperties and could work as an isolating barrier on a custom-made PCB.

According to another preferred embodiment of a plug device according tothe invention, one or more of said isolating barriers are attached to orheld in place by one of said components on said PCB and not said housingor directly on said PCB which makes it possible to arrange components onsaid PCB in a way in which it would be difficult to attach saidisolating barriers to said PCB or said housing.

According to another preferred embodiment of a plug device according tothe invention, a signal transformer is used instead of an optocoupler.The function of said optocoupler is to send a signal from thelow-voltage side to the high-voltage side while having a galvanicseparation.

According to another preferred embodiment of a plug device according tothe invention, the signal transformer is integrated into thehigh-frequency transformer In this way, only a single magnetic core isused to form a component with a dual purpose and thus saves space.

Placing the PCB perpendicular to the input connectors and perpendicularto the side surface of the plug device gives some advantages and istherefore preferred. This is not a straightforward solution because thisorientation results in a smaller PCB surface area than with the othertypes of orientation. The arrangement of the PCB allows for the use ofcapacitors of radial type which usually are cylindrical and have bothconnectors at the same end of the component and therefore occupy asmaller space on the PCB. Capacitors with connectors at each end mayalso be used but they are less convenient.

Using the above described isolating barriers and with the preferredarrangement of said PCB, it is possible to manufacture a plug device ofEuropean type dimensions with a built-in adapter of the SMPS type, whichcomplies with the IEC-STANDARDS for devices of this type. It is alsopossible to use standard-type capacitors and other components whilestill remaining within the dimensions of a plug device of a Europeantype.

DRAWINGS

FIG. 1 shows a prior art wall adapter with a linear type adapter.

FIG. 2 shows a prior art wall adapter with the SMPS type adapter.

FIG. 3 shows the interior arrangement of the PCB, in a prior art walladapter with SMPS type adapter.

FIG. 4.1 shows a first arrangement of a PCB in a European type plugaccording to the invention.

FIG. 4.2 shows a second arrangement of a PCB in a European type plugaccording to the invention.

FIG. 4.3 shows a third arrangement of a PCB in a European type plugaccording to the invention.

FIG. 5 shows a PCB with the arrangement of the largest componentscomprising a SMPS according to the invention.

FIG. 6 shows the PCB provided with slots according to the invention.

FIG. 7 shows a section view of the PCB with the largest componentscomprising an SMPS within the housing of the plug device according tothe invention.

FIG. 8 shows the isolating barriers extending from the housingsaccording to the invention.

FIG. 9 shows a section view of the input connectors, the fuse componentand the isolating barrier for the fuse component according to theinvention.

FIG. 10 shows a schematic view of a generic, flyback, switch-mode powersupply circuit.

FIG. 11 shows a schematic view of a flyback, switch-mode power supplycircuit adapted to deliver 3 W power.

FIG. 12 shows a schematic view of a flyback, switch-mode power supplycircuit adapted to deliver 3 W power.

FIG. 13 shows a schematic view of a flyback, switch-mode power supplycircuit adapted to deliver 5 W power.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, the same reference numbers areused for the same components unless otherwise stated.

The prior art wall adapter 10 shown in FIG. 1 is an approximation tomost wall adapters used for mobile phones and the like. This walladapter 10 uses linear technology. Input connectors 12 and 14 areattached to a connecting body 16. The connecting body has the shape of aEuropean-type plug. A main body 18 encloses the transformer, diodes,capacitors and other necessary components. As it appears, the main body18 of the wall adapter 10 is large and may easily obstruct one or moreadjacent wall sockets. In some wall adapters, the main body 18 is offsetwith regard to the connecting body 16 making it possible to arrangeother plugs in one adjacent socket.

FIG. 2 shows a prior art wall adapter 20 using the SMPS type convertingtechnology.

As with the wall adapter 10 shown in FIG. 1, the input connectors 12 and14 are attached to a connecting body 16, which has the shape of aEuropean type plug and a main body 22. The SMPS is housed within themain body 22 of the wall adapter 20. All of the components are arrangedon a PCB 24 in the main body 22, as shown in FIG. 3, and the inputconnectors 12 and 14 are connected to the PCB 24 either in the main body22 or in the connecting body 16 (not shown). The size of the main body22 using SMPS-technology is usually smaller than the main body 18 of thewall adapter 10 shown in FIG. 1, but is usually still much larger than aEuropean type plug.

As explained above, the invention relates to a plug device of a Europeantype size with a built-in power supply of the SMPS type. A plug device30 of this type comprises input connectors 12 and 14 attached to ahousing 26 of approximately European-type plug size or the size of theconnecting body 16 in FIGS. 1 and 2. To be able to arrange a powersupply within a plug device of this type, space for a PCB 24 and thecomponents comprising the power supply is required. FIG. 4.1, 4.2 and4.3 show three possible orientations of a PCB 24 inside the housing 26of the plug device 30.

The components that have to be arranged on the PCB 24 can roughly-bedivided in two groups: Control components, which generally are small,and power components, which generally are large. These have to bearranged on the PCB 24 in a way which makes the circuit function asintended and at the same time makes it possible to comply with therequired standards for isolation and EMC. As shown in FIG. 5, thehigh-voltage capacitor 34, the high-frequency transformer 32 and thelow-voltage capacitor 28 are the LARGEST components and arranged on thesame side of the PCB 24 with the capacitors 28 and 34 at each end andthe high-frequency transformer 32 in-between. In this way, the PCB 24 isdivided into a high-voltage part and a low-voltage part. Thehigh-frequency transformer 32 is arranged closely to the high-voltagecapacitor 34 and with a small gap to the low-voltage capacitor 28. Thegap between the high-frequency transformer 32 and the low-voltagecapacitor 28 thus makes it possible to insert a first isolating barrier36 between them. The first isolating barrier 36 is in the form of an Lso that a leg thereof is able to extend over the top of thehigh-frequency transformer 32 making it possible to have low-voltageconnections over the high-frequency transformer 32 while maintaining therequired isolation. Also shown on the figure is the second isolatingbarrier 38 that extends between the high-frequency transformer 32 andthe PCB 24.

In this way, the second isolating barrier 38 shields the optocoupler 40which is shown arranged beneath or approximately beneath thehigh-frequency transformer 32 from the conducting surface of the core ofthe high-frequency transformer 32.

It is the insertion of isolating barriers, which enables the isolationbetween the high-voltage side and the low-voltage side to meet therequirements of the standards. To accommodate further barriers, twoslots 42,44 are made in PCB 24 as shown in FIG. 6. The slots 42,44 aremade in the PCB 24 at a position between the connectors of thehigh-frequency transformer 32, thereby dividing the PCB 24 into ahigh-voltage part and a low-voltage part. The third and fourth barrierwalls 46 and 48 inserted into a slot in the PCB 24 thus increases theclearance distance between high-voltage side and low-voltage side. Thebarriers also help with creepage distance because the surface distancebetween the high-voltage side and the low-voltage side become longervoltage Between the slots 42,44 and beneath the high-frequencytransformer 32, the optocoupler 40 is arranged as shown in FIG. 7 andthus the only two components which span the isolation gap between thehigh-voltage side and the low-voltage side are the high-frequencytransformer 32 and the optocoupler 40. It is also possible to arrangethe optocoupler 40 on the opposite side of the PCB 24 if it is difficultto arrange it on the same side as the high-frequency transformer 32voltage FIG. 8 only shows one half of the housing 26 for greatervisibility. There are a number of isolating barriers which extend outfrom the housing 26. These isolating barriers either form an integratedpart of the housing 26 or are attached to the housing 26. The benefit ofnot attaching the isolating barriers to the housing 26 is that theisolating barriers may be made from a different material than thehousing 26 and thus have different isolating properties than the housing26. The shown isolating barriers correspond to the ones described inconnection with FIGS. 5,6 and 7. The two isolating barriers 36 and 38may optionally be formed as two shorter isolating barriers that extendfrom each side of the housing 26 and overlap each other in the middle,thus forming a complete isolating barrier. If the latter is the case,the half of the housing 26 shown in FIG. 8 and the half not shown mayform an approximate mirror of each other. Otherwise the only isolatingbarrier which extends from the half of the housing 26 not shown in FIG.8 is the fourth isolating barrier 48 voltage FIG. 9 shows how a fifthisolating barrier 52 is arranged in connection with a fuse component 50.The plug device is shown with the PCB 24 as arranged in FIG. 4.1.

The fuse component 50 is connected between one of the input connectors12 or 14 and the PCB 24. As it appears, the fifth isolating barrier 52extends partially around the fuse component 50, thus isolating it fromthe remaining components comprising the SMPS. Alternatively, theisolating barrier 52 could extend all the way around the fuse component50. Another alternative is to arrange the fuse component with an offsetto the centerline of the PCB 24, thus leaving more room for componentsto be arranged on the PCB 24 facing the fuse component 50. The housing26 further has a low-voltage output cord with an attached strain relief54.

In FIG. 10 a schematic view of a generic, flyback, switch-mode powersupply circuit is shown. The circuit comprises a safety fuse, arectifier, an energy reservoir filter section, a clamp circuit section,a transformer, a switch controller, a safety capacitor, a feed-backopto-coupler, a rectifier section and a secondary energy reservoircapacity.

FIG. 11,12 and 13 are schematic views of three prototypes of the genericflyback, switch-mode power supply circuit of FIG. 10 adapted to deliver3,3 and 5 watts output, respectively. FIG. 1 1 and 13 illustratesoptocoupler feedback-based, flyback, switch-mode power supply circuits.FIG. 12 illustrates a transformer feedback-based flyback switch-modepower supply circuit. The components used to assemble the prototypes arelisted in example 1,2 and 3.

In the description of the invention a European-type plug has been usedas an example, however, the invention may easily be adapted for e.g. usewith different shaped input connectors, like American or British plugdevices.

The invention has been described where an SMPS is build into a plugdevice.

However, as the invention relates to an SMPS with small dimensions, itis possible to make a number of changes while remaining within the ideaof the invention. As an example, it is possible to attach a second setof connectors to the housing as the low-voltage output. The plug devicecould then fit into a socket on, e.g. a PCB or in a device and thus actas a low-voltage supply. Another example is when the input connectorsare adapted for other kinds of connections and the plug device may actas the power supply in devices such as shavers, light bulbs, bicyclelamps and the like.

EXAMPLE 1

In a prototype implementation of the power supply circuit shown in 11,the following elements and components were used.

A capacitor 34,6, 8 uF, 400V, from Rubycon.

A capacitor 56, MLCC SMD0603, from Phycomp.

A capacitor 28, 1000 uF, 10V, from Luxon.

A capacitor 60, 33 uF, 10V, from Luxon.

A capacitor 58,56 nF, 1000V, from Johanson.

A capacitor 62, MLCC, SMD0603,220 nF, 50V from AVX.

A capacitor 64, MLCC, SMD1206,100 nF, 100V, from Phycomp.

A zener diode 66, from ON Semiconductor.

A Schottky diode 68,2A, 40V, 0.3V, 100 pF, from ON Semiconductor

A rectifier bridge 70 from Diotec.

A diode 72,600 Vrrm, 0.5 A, from Diotec.

A 10 ohm, 2 W, wire wound fusible resistor 74 from Token.

A RF choke 76, 1000 uH, 139 mA, from Epoos.

A chip Inductor 78, 1 uH, 1000 mA, from Murata.

An optocoupler 40, from NEC.

Three resistors 80,82, 84, SMD 0603,0.063W, 50V from Phycomp.

Two resistors 86,88, SMD 0402,0.05 mW, from Phycomp.

A switch element 90 from Power Integrations.

A transformer 32, EF12.6, TEX-E wire, custom made.

A capacitor 92,330 pF, 250V, 4000V, from BC components.

A 1 mm thick, 2-layer PCB, custom made.

A bottom plastic casing, weighing 2.8 gram, custom made.

A top plastic casing, weighing 2.9 grams, custom made.

Two brass pins, each weighing 1.3 grams.

A low profile spring loaded contact, from Preci Dip.

EXAMPLE 2

The above-mentioned components may also be assembled to form atransformer-based flyback switch-mode power supply circuit, omittingsome components from the listing in example 1. In FIG. 12 the referencenumerals refer to the components listed in example 1.

EXAMPLE 3

In a prototype implementation of the power supply circuit shown in 13,the following elements and components were used.

A capacitor 34,6, 8 uF, 400V, from Rubycon.

A capacitor 94, MLCC, 1 nF, 200V, X7R, from AVX.

A capacitor 96, MLCC, 100 nF, 50V, from Phycomp.

A capacitor 28,1000 uF, 10V, from Luxon.

A capacitor 60,33 uF, 10V, from Luxon.

A capacitor 58,56 uF, 1000V, from Johanson.

A zener diode 66, from ON Semiconductor.

A Schottky diode 68,2A, 40V, 0.3V, 100 pF, from ON Semiconductor.

A rectifier bridge 70 from Diotec.

A diode 72,600 Vrrm, 0.5 A, from Diotec.

A 10 ohm, 2 W, wire wound fusible resistor 74 from Token.

A RF choke 76, 1000 uH, 130 mA, from Epcos.

A chip Inductor 78, 1 uH, 1000 mA, from Murata.

An optocoupler 40, from NEC.

Two resistors 98,100 SMD 0805,0.125 W, 150V from Phycomp.

Five resistors 86,88, 102,104, 106, SMD 0402,0.05 mW, from Phycomp.

A switch element 90 from Power Integrations.

A transformer 32, EF12.6, TEX-E wire, custom made

A capacitor 92,330 pF, 250V, 4000V, from BC components.

An operations amplifier 108,0.9-7 V, from ON Semiconductor.

A resistor 112,2M Ohm.

A resistor 110,0, 047 Ohm.

A 1 mm thick, 2-layer PCB, custom made.

A bottom plastic casing, weighing 2.8 gram, custom made.

A top plastic casing, weighing 2.9 grams, custom made,

Two brass pins, each weighing 1.3 grams.

A low profile spring loaded contact, from Preci Dip.

The invention is further characterised by the following points.

1. Plug device with a built-in power supply of the switch mode powersupply type comprising a printed circuit board (244) upon which ahigh-frequency transformer (32), a low-voltage capacitor (28) and othercomponents are arranged, said device further comprising a housing (26)and at least two input connectors (12,14) adapted for insertion into awall socket characterised in that a first isolating barrier (36) extendsfrom said housing (26) in between said high-frequency transformer (32)and said low-voltage capacitor (28).

2. Plug device according to point I upon which a low-voltage output cord(54) is attached and adapted for connecting said plug device to aconsumer, characterised in that said first isolating barrier (36) alsoextends between said high-frequency transformer (32) and saidlow-voltage cord (54).

3. Plug device according to point 1 characterised in that a thirdisolating barrier (46) extends from said housing (26) and into a firstslot (42) in t!he said printed circuit board (24) and a fourth isolatingbarrier (48) extends from said housing (26) and into a second slot (44)in said printed circuit board (24) and that said first and second slots(42,44) are arranged between the high-voltage and low-voltage connectionterminals of said high-frequency transformer (32).

4. Plug device according to point 1 CHRACTERISED in that an optocoupler(40) is arranged on said printed circuit board (24) between said firstand second slots (42,44) beneath said high-frequency transformer (32)and on the same side of said printed circuit board (24) as saidhigh-frequency transformer (32),

5. Plug device according to point 1 characterised in that an optocoupler(40) is arranged on said printed circuit board (24) between said firstand second slots (42,44) beneath said high-frequency transformer (32)and on the opposite side of said printed circuit board (24) as saidhigh-frequency transformer (32).

6. Plug device according to point 1, 4 or 5 characterised in that asecond isolating barrier (38) extends from said housing (26) and betweensaid high-frequency transformer (32) and said printed circuit board (24)and any other components arranges on said printed circuit board (24)beneath or approximately beneath said high-frequency transformer (32).

7. Plug device according to any of the preceding claims upon which afuse component (50) is attached between one of said at least two inputconnectors (12,14) and said printed circuit board (24) characterised inthat a fifth isolating barrier (52) extends from said housing (26) andfully or partially around said fuse component (50).

8. Plug device according to any of the preceding claims characterised inthat said housing (26) and said isolating barriers (36,38, 46,48, 52)are moulded as one piece.

9. Plug device according to any of the preceding claims characterised inthat said housing (26) is comprised of two or more separate piecesadapted for attaching each other and forming a larger element.

10. Plug device according to point 9characterised in that one or more ofsaid isolating barriers (36,38, 46,48, 52) are separate pieces from saidhousing (26) and attached to or held in place by said housing (26).

11. Plug device according to point 10characterised in that said housing(26) and said isolating barriers (36,38, 46,48, 52) are constructed frommaterials with different material properties.

12. Plug device according to point 3, 4 or 5 characterised in that saidslots (42,44) in said printed circuit board (24) extends all the wayover said printed circuit board (24) dividing it in two parts.

13. Plug device according to any of the preceding claims characterisedin that one or more of said isolating barriers (36,38, 46,48, 52) areattached to or held in place by said printed circuit board (24) and notsaid housing (26).

14. Plug device according to any of the preceding claims characterisedin that one or more of said isolating barriers (36,38, 46,48, 52) are anintegrated part of said printed circuit board (24) and not said housing(26).

15. Plug device according to any of the preceding claims characterisedin that one or more of said isolating barriers (36,38, 46,48, 52) areattached to or held in place by one of the components on said printedcircuit board (24) and not said housing (26) or said printed circuitboard (24). 16. Plug device according to any of the preceding claimscharacterised in that a signal transformer is used instead of anoptocoupler.

17. Plug device according to point 15 CHARACTERISED in that said signaltransformer is integrated into said high-frequency transformer (32).

1. A power supply unit comprising: a housing defining a front end and arear end, a pair of pins for co-operating with a mains supply outlet andextending perpendicularly from a front end wall of said front end ofsaid housing, a low-voltage cord or a low-voltage connector extendingfrom said rear end of said housing, a switch mode power supply circuitincluding a printed circuit board for the conversion of the mains supplyvoltage to a low-voltage, said printed circuit board being mountedwithin said housing oriented substantially parallel with said front endwall having said pins connected to the one side of said printed circuitboard and having said low-voltage cord or low-voltage connectorconnected to said one side or preferably the opposite side of saidprinted circuit board, and said housing having a cross-sectionalconfiguration between said front end and said rear end, substantiallycorresponding to and not exceeding the cross-sectional configuration ofthe front end wall of a Euro-plug according to the EN 50075 standard. 2.The power supply unit according to claim 1, said switch mode powersupply circuit including a first rectifier or mains supply rectifier forreceiving said mains supply voltage and for converting said mains supplyvoltage into a first DC voltage to be output from a pair of outputs ofsaid first rectifier, a first energy reservoir capacitor connectedacross said outputs of said first rectifier for smoothing said first DCvoltage, a high frequency oscillator or high frequency switch having apair of input terminals for receiving said first DC voltage from saidenergy reservoir capacitor and for output of a high frequencyoscillation voltage from a pair of output terminals to a high frequencytransformer for reducing the voltage of said high frequency oscillationinto a low transformer output voltage and having a pair of inputterminals and a pair of output terminals, said input terminals beingconnected to said output terminals of said high frequency oscillator orhigh frequency switch, said output terminals of said high frequencytransformer being connected to a further rectifier for rectifying saidtransformer output voltage and having a pair of rectifier outputs forconnection to a further energy reservoir capacity connected to saidlow-voltage cord or said low-voltage connector.
 3. The power supply unitaccording to claim 1, said switch mode power supply circuit furtherincluding an input fuse establishing connection from one of said pins tosaid printed circuit board.
 4. The power supply unit according to claim1, one of said pins being connected to a spring bias contact element ofsaid printed circuit board for establishing electrical conductiveconnection from said pin to said switch mode power supply circuit. 5.The power supply unit according to claim 1, said high frequencytransformer being positioned between said two capacitors on said printedcircuit board facing away from said pair of pins.
 6. The power supplyunit according to claim 1, said housing further having a first inwardlyprotruding isolating barrier extending from said housing into an innerspace defined within said housing and in between said high frequencytransformer and said low-voltage capacitor.
 7. The power supply unitaccording to claim 6, said first isolating barrier further extending inbetween said high frequency transformer and said low-voltage cord orlow-voltage connector.
 8. The power supply unit according to claim 6,said housing including a further inwardly protruding isolating barrierextending into said inner space defined within said housing and into aslot in said printed circuit board.
 9. The power supply unit accordingto claim 1, said isolating barrier or isolating barriers beingintegrally moulded with said housing, or alternatively, said housingbeing filled out with an isolating filling substance.
 10. The powersupply unit according to claim 1, said printed circuit board having oneor more through-going apertures partly or completely dividing saidprinted circuit board into two or more parts.